Your daughter is way too young to be diagnosed with ODD as a primary diagnosis. At her age, ODD is a diagnosis used when there is no real diagnosis identified. It describes behavior. Her behavior, though, doesn't fit ODD. It is too specific to you and the family dynamics, not to general behavior. In other words, it is relationship based and that's why it was identified as separation anxiety originally.
It's possible that your daughter will "graduate" to ODD. But let's hope not. I know that you are desperate to have some sort of explanation to give the frustrating hellishness of it all some sense. But if your daughter gets labeled with ODD, it will follow her throughout school and adolescence and can become a self fulfilling prophecy where she will begin to act with everyone like she's acting with you. At least now, she's expressing some primal feelings that have to do with a long ago separation she never got over. That's much better than ODD, though I know it doesn't seem like that for you.
Your effort with rewards is way too intellectualized for her. That's why I urge you to do this with a therapist advising you who has gotten to know her. Remember, whatever the internal forces driving this behavior, she is not consciously doing this. My experience tells me this is almost certain. She is more frustrated than you are. She doesn't know HOW to change her behavior because it is not consciously being done.
So, the behavior modification techniques have to be much more impulse control oriented. That means immediate reinforcement for positive behavior. Behavioral Therapy is not just about rewards. It is about reinforcing the desirable behavior. Rewards can help. But all reinforcements are necessary: praise, soothing, etc.
Please don't give up on her. Work with a therapist who you think is smart and kind. And as for the other kids, have a family meeting with them without her. Discuss the problem without getting too much into details, just briefly about her having a long term problem from when she was 2 because of trauma of you leaving. Explain that it isn't that she gets away with things. It's that she has a problem. And that you need them to be part of the family, helping her by not acting as if she's getting away with something. And helping you by not taking advantage. Stress
that you're a family and that this isn't your problem with her. That as a family everyone needs to understand that she has a problem and that you are all on her side, praying for her (if your family prays) and being helpful to let her see how things should be. And let them know how much you love them and that you know that she takes up a lot of your energy but that they shouldn't think that they aren't as important to you, etc. The younger kids: make it simple for them. Address the older kids more. And you might ask the therapist if there could be some family sessions to help as well.
You see, my approach is that your daughter has a problem that we don't want to spread into her being labeled as a problem kid. And so the whole family may have to pitch in as well.
I wish you the very best!
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